SUMMARY ? Overview Modeling of infectious diseases that affect the human central nervous system (CNS), such as those associated with Zika virus (ZIKV) and West Nile virus (WNV), has been challenging due to the inaccessibility of the relevant cell types. Reprogramming human somatic cells, such as skin fibroblasts, into induced pluripotent stem cells (iPSCs) provides a genetically tractable and renewable source of human neural cell populations. We can differentiate these iPSCs into many of the cell types critical for the study of neurotropic viruses, but typically this is performed in monolayer cultures to allow for more control and to generate more homogeneous cell populations, but this methodology lacks the self-organizing properties and interactive dynamics among different cell populations observed during organ development. Recently, more complex structures resembling whole developing organs, named organoids, have been generated from human iPSCs via 3D culturing methods. This emerging new technology has the potential to significantly advance our understanding of infectious diseases and for future therapeutic development. The success of this approach, however, critically depends on how well organoids mimic biological structures, recapitulate human physiology and disease pathology, and incorporate components critical to disease and human host responses. We propose to develop a robust platform for organoid development to model brain development that can be adopted by single labs for basic research, and is amenable to translational studies and drug development and testing. Our Research Center is comprised of three Research Projects, a Scientific Core, and an Administrative Core led by experts in virology, stem cell biology, neural development, and bioengineering. We will focus on ZIKV and WNV, two neurotropic flaviviruses, to develop our organoid platform, which can then be used by the scientific community to investigate other infectious diseases that affect the nervous system. Importantly, ZIKV and WNV are thought to impact the CNS at different stages of development, with ZIKV having been recently implicated as being causal for microcephaly in some pregnant women. This affords us the opportunity to develop an organoid platform with proof-of-principle testing with viruses suspected to have cell type- and stage-specific tropism. Project 1 will focus on technology development to generate more mature organoids and the scaling up of robust assays to perform medium-throughput compound testing. Project 2 will focus on ZIKV infections in early stage organoids and Project 3 will evaluate co-culture organoid systems to model WNV infections in later stage organoids. The projects will be supported by a Scientific Core that will provide cells and on-site training to Projects 2 & 3, as well as optimization of differentiation protocols and bioinformatics analyses. Finally, the Administrative Core will provide logistical support to facilitate collaborations among investigators and to coordinate the timely release of results and resources to the scientific community.